This invention relates to a variable displacement pump arranged to supply a hydraulic fluid to sliding portions and so on of an internal combustion engine for a vehicle.
U.S. Patent Application Publication No. 2008/308062 (corresponding to Japanese Patent Application Publication No. 2008-309049) discloses a conventional variable displacement oil pump which is employed as a hydraulic pressure source of an internal combustion engine and so on of a vehicle. This conventional variable displacement oil pump controls an eccentric amount of a cam ring constantly urged by a spring in an eccentric direction with respect to a center of a rotation of a rotor, based on a discharge pressure introduced into a control hydraulic chamber separated between a housing and a cam ring. With this, this variable displacement oil pump varies the discharge amount so as to attain the energy saving by decreasing the driving torque of the pump.